144 MALARIA 



filiform bodies, which actively swim about seeking 

 a female gametocyte (Fig. 2, i). When found they 

 fuse with it, and thus produce a fertilized cell or 

 zygote (Fig. 2, 3). This zygote is produced on the 

 microscope-slide, and in the alimentary canal of certain 

 mosquitoes, but so far as is known at present it under- 

 goes further development only in the stomach of the 

 various species of the mosquito genus Anopheles. In 

 all other cases it dies or is digested. In Anopheles, 

 however, the zygote travels to the walls of the 

 stomach, pierces the inner coats and comes to rest 

 underneath the muscular tunic which ensheaths that 

 organ (Fig. 2, 4 and 5). 



At first the zygote is very small, about the size of 

 a red blood-corpuscle ; but it grows, and in the course 

 of about a week it has, roughly speaking, increased to 

 five hundred times its original bulk (Fig. 3, i and 3). 

 Its contents have not only increased, but have divided 

 into some eight or twelve cells, called meres ; and 

 each of these meres has given off round its periphery 

 a number of filiform cells, called blasts (Fig. 3, 2). 

 The structure of the mere, with its coating of blasts, 

 may be easily understood by a zoologist when it is 

 mentioned that it very closely resembles that stage in 

 the formation of the spermatozoa of the earth-worm 

 just before the spermatozoa separate themselves from 

 the blastophor ; the lay mind may gain a better idea 

 of its appearance by recalling the head of a mop. As 

 the zygote, still resting on the outside of the mos- 

 quito's stomach, matures, the cells which are giving 

 rise to the blasts diminish in size and disappear, 

 leaving the capsule packed with thousands of minute 

 filiform slightly spindle-shaped blasts (Fig. 3, 3). 

 Then the capsule bursts and the blasts make their 

 way into the body-cavity, or space between the 

 stomach and the wall of the mosquito's body. It is 

 not known whether they have any movement of their 



